The present invention relates to phased arrays of antennas and, in particular, to methods and devices for achieving wide spatial scan performance over a broad range of frequency bands therewith.
The current method of achieving wide scan performance over broad frequency bandwidth in patch-based scanning apertures is to use substrates with low dielectric constant, such as foam. Unfortunately, these low dielectric constant substrates are often not mechanically or environmentally robust, and they do not allow for the extremely small processing tolerances required by the increasing operating frequency of phased array systems. More suitable substrate materials, which inherently have higher dielectric constants, limit the achievable bandwidth and scan volume of phased arrays due to induced surface waves that can cause the well-known scan blindness problem seen in the art.
Furthermore, phased array apertures comprised in part of dielectric substrates over a ground plane are subject to performance degradation due to surface waves. Metamaterial structures, such as electromagnetic band-gap structures (EBGs; referred to herein generally as metamaterials) have been proposed in the literature to be integrated into the aperture to suppress surface waves and therefore improve the scanning performance of the aperture. Such systems are described in, for example, U.S. Pat. No. 7,773,033 to Morton, et al., incorporated herein by reference in its entirety. However, interactions between the phased array antenna elements and the elements of the EBG structure can cause undesired modes in the aperture that also can degrade aperture performance. These interactions must be suppressed in order to take full advantage of the benefits of the EBG structure.
One known approach to suppressing these interactions is to lower the dielectric constant of the substrate covering the ground plane in order to remove the necessity of the EBG structure. However, advanced phased arrays benefit from higher dielectric constants so this approach is undesirable.
Scan blindness, and prior attempts at amelioration with metamaterial/EBG structures are described in, for example, the following references, each of which is hereby incorporated herein by reference in its entirety:                Yunqi Fu and Naichang Yuan, “Elimination of Scan Blindness in Phased Array of Microstrip Patches Using Electromagnetic Bandgap Materials,” IEEE Antennas and Wireless Propagation Letters, Vol. 3, 2004;        Zeev Iluz, et al., “Microstrip Antenna Phased Array with Electromagnetic Bandgap Substrate,” IEEE Trans. Antennas and Propagation, Vol. 52, No. 6, Jun. 2004; and        Lijun Zhang, et al., “Scan Blindness Free Phased Array Design Using PBG Materials,” IEEE Trans. Antennas and Propagation, Vol. 52, No. 8, Aug. 2004,        